A photographic system where a photographic element comprising silver halide grains is used for recording an image followed by development to reproduce and store a photographic image has been developed significantly in recent years and is now applied in various technical fields. Above all, the market for color photographs, which are utilized by many people for the purpose of recording and seeing images, is expanding year by year. In particular, in color print production, the demand for the delivery of finished prints in a short amount of time is increasing rapidly. As a result, the need for the production of color prints with high efficiency and high producibility is rising steadily.
As is well known, the process of finishing color prints comprises exposure of a printing photographic material to be effected through an image-recorded negative film and color development of the exposed photographic material. Use of a high-sensitivity photographic material results in shortening the exposure time. Therefore, in order to shorten the color development time, it is essential to use a photographic material which may be rapidly developed.
A known means for attaining the above-mentioned qualities is a method of processing a color photographic paper containing a so-called high silver chloride emulsion having an elevated silver chloride content, in place of a high silver bromide emulsion having a high silver bromide content, which has heretofore been widely incorporated in conventional color printing photographic materials (hereinafter referred to as a "color photographic paper"). For instance, International Laid-Open Patent Application WO87-04534 has disclosed a method for rapidly processing a color photographic paper which contains a high silver chloride emulsion using a color developer which does not substantially contain a sulfite ion and a benzyl alcohol.
For the purpose of obtaining a photographic system which may be processed rapidly, attempts to put silver halide emulsions having a high silver chloride content into practical use have previously been made actively. In general, it is known that a high silver chloride emulsion often involves the generation of much fog and cannot have a high sensitivity. It is also known that such an emulsion often involves the so-called reciprocity law failure of fluctuation of the sensitivity and gradation thereof, which is caused by variation in the intensity of light which is applied thereto for exposure. In addition, it is also known that the sensitivity of such an emulsion often fluctuates due to variations in the ambient temperature during exposure. These drawbacks have been significant impediments to the practical use of high silver chloride emulsions.
Various technical means for overcoming the above-mentioned drawbacks of high silver chloride emulsions have previously been reported.
For instance, JP-A-58-95736, JP-A-58-108533, JP-A-60-222844 and JP-A-60-222845 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") disclose various high silver chloride emulsions of various grain structures, which contain silver halide grains each having a layer having a high silver bromide content so as to have a high sensitivity while retarding fogging of the emulsion. By the present inventors' investigation of the disclosed technology, however, it has been found that such high silver chloride emulsions do have a high sensitivity, but they are easily desensitized when pressure is applied to the emulsion grains. Such poor pressure resistance of the grains has been found to be a fatal defect for practical use of the grains.
JP-A-51-139323 and JP-A-59-171947 and British Patent 2,109,576A describe high-sensitivity silver halide emulsions containing a compound of a group VIII metal, and such emulsions are free from reciprocity law failure. JP-A-49-33781, JP-A-50 23618, JP-A-52-18310, JP-A-58-15952, JP-A-59-214028, JP-A-61-67845, German Patents 2,226,877, 2,708,466 and U.S. Pat. No. 3,803,584 describe silver halide emulsions, which may yield hard images and which are free from reciprocity law failure, that are obtained by incorporating a rhodium compound or iridium compound into the emulsion. However, while emulsions containing a rhodium compound do yield hard images, they are also noticeably desensitized and thus they are unfavorable for practical use. On the other hand, emulsions containing an iridium compound notably involve the so-called latent image sensitization, which involves an increase in the developed density when a period of time passes between the exposure of the photographic material having the emulsion and the processing thereof. Therefore, such emulsions are also unfavorable for practical use.
U.S. Pat. No. 4,269,927 describes surface latent image-type high silver chloride emulsion grains having a silver chloride content of 80 mol % or more where the sensitivity is elevated by the incorporation of cadmium, lead, copper, zinc, or a mixture thereof, into the inside of the emulsion grains. While using such emulsion grains may achieve some results towards increasing the sensitivity and removing the reciprocity law failure, the sensitivity fluctuations of these emulsions due to variations in the ambient temperature during exposure could not be fully overcome.
JP-B-48-35373 (the term "JP-B" as used herein means an "examined Japanese patent publication") describes a hard black-and-white printing paper which is inexpensively produced by incorporating a water-soluble iron compound into a silver chloride emulsion obtained by a normal mixing method. In accordance with the disclosed means, the high intensity sensitivity of the silver chloride emulsion can be elevated, but the sensitivity fluctuations of the emulsion due to variations in the ambient temperature during exposure could not be fully overcome and, in particular, the temperature dependence of the emulsion's sensitivity during high intensity exposure could not be fully overcome.
JP-A-1-183647 describes that addition of a silver bromide local layer to the inside or the surface of high silver chloride emulsion grains which contain iron ions results in elevation of the emulsion grains' sensitivity, and that sensitivity fluctuations due to variations in the ambient temperature during exposure may thereby be reduced. However, the disclosed technology is not sufficient to overcome the temperature dependence of the emulsion grain sensitivity during high intensity exposure.